UV irradiation of flowing liquids is undertaken for various purposes, for example to disinfect drinking water and waste water, and to trigger chemical reactions which are enabled by the UV radiation. The UV dosage given to each volume element is always decisive for the desired effect of the UV radiation in the liquid. In disinfection applications, the microorganisms contained in the water are reliably disinfected only if a specific minimum dosage is applied to them. It is therefore necessary to set the radiation power in the system in such a way that the liquid volume with the shortest residence time or the lowest irradiation intensity reliably receives the required minimum dosage of UV radiation.
This means that, with a strongly inhomogeneous flow within the UV reactor, the slowly flowing volume elements receive too high a dosage, i.e. too much energy is expended in this area if the fastest-flowing volume elements are reliably to receive a dosage above the required minimum dosage. A substantial part of the operating costs of a system of this type for disinfecting drinking water is incurred by the power consumption of the UV radiators which are used. Efforts are made to design the flow through a UV reactor of this type to be as even as possible, so that all volume elements receive roughly the same radiation dosage.
Various solutions are proposed for this purpose. Systems exist which comprise elongated UV radiators of the mercury low-pressure radiator type, which are disposed parallel to the flow in the UV reactor. In these systems, the radiation is swirled, for example, by means of baffle plates, in such a way that all liquid volumes come into the vicinity of the radiators, thereby achieving a substantially even irradiation of the entire flowing liquid. These baffle plates increase the flow resistance of the system and reduce the possible liquid throughput. A device of this type is presented, for example, in the publication U.S. Pat. No. 5,352,359, which is incorporated by reference.
A different approach consists in the homogenisation of the flow within the UV reactor. To do this, static mixers are used to homogenise the speed distribution or the speed profile within the flow. A technical solution of this type is presented in the patent document U.S. Pat. No. 7,018,544 B2, which is incorporated by reference. This solution also increases the flow resistance. It is furthermore dependent on a flow entering in a roughly straight line with a rotationally symmetrical speed profile.